Feel means for pressure fluid follow-up servomotor



c. R. CHURN 2,488,173

2 sheets-sheet 1 \b 2 2 3.3 on N FEEL MEANS FOR PRESSURE FLUID FOLLOW-UP SERVOMOTOR N\ 3 ON QN Nov. 15,1949

Filed Feb. 18, 1947 MN Hm RN mm mm Nov. 15, 1949 C. R. CHURN FEEL MEANS FOR PRESSURE FLUID FOLLOW-UP SEBVOMOTOR 2 SheetsSheet 2 Filed Feb. 18, 194"! 1/ um 8 NW mm 3 6 95. G 2 N. a u UFK Patented Nov. 15, 1949 FEEL MEANS FOR PRESSURE FLUID FOLLOW-UP SERVOMOTOR Charles Reginald Churn, Tilehurst, England, assignor to The Fairey Aviation Company Limited, Hayes, England Application February 18, 1947, Serial No. 729,286

In Great Britain January 24, 1946 Claims.

It is known that balanced manually-operated ailerons on an aircraft produce, on the pilots control, an effort varying in magnitude with the speed of the aircraft and which, by resisting the pilots efiort, gives him a sense of feel of which he is robbed if the ailerons are power-operated. The object of the present invention is to restore this sense of feel by inducing a reaction proportional to the total actuating efiort required, and although it will be described with reference to the power actuation of aircraft control surfaces, it is not restricted thereto, and may be employed in the power actuation of any other control surfaces where a similar sense of feel is desirable, for instance, on the rudder of a boat.

7 To this end and in accordance with the present invention hydraulic servo means for actuating a control surface comprise a jack cylinder, a jack piston connected with the control surface to be actuated, a selector valve for the jack and a reaction piston within the jack piston, the pilots control being connected directly with the selector valve and through a lost motion device with the reaction piston, the arrangement being such that the fluid pressure admitted to the jack acts also, in the opposite direction, against the reaction piston to produce a sense of feel at the pilot's control.

The jack piston may be formed with internal stops to limit the travel of the reaction piston relatively to said jack piston, so as to provide direct manual control if the hydraulic pressure fails.

Alternatively, the reaction piston may be formed with an external and an internal stop near the point where it merges from the jack piston to coact with said jack piston and thus limit the travel of the reaction piston relatively to said jack piston, so as to provide direct manual control if the hydraulic pressure fails.

In another alternative, the jack cylinder instead of being directly secured, e. g. to the aircraft, may be slidably mounted in an anchorage and normally locked relatively thereto under the action of the hydraulic pressure, but may be releasable therefrom if the hydraulic pressure fails, and may be permitted to move axially relatively to said anchorage to provide direct manual control if the hydraulic pressure fails.

The jack cylinder may be formed with a circumferential groove and the anchorage may be provided with a collet arranged to be movable radially inwards by a piston to engage said groove and so anchor the jack cylinder under the influence of the hydraulic'pressure acting on the 2 piston, but, if the hydraulic pressure fails, to be movable radially outwards out of the groove under spring pressure, so releasing the jack body relatively to the anchorage.

Four forms of the invention as applied to aircraft will be described with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic sectional elevation of one form,

Figure 2 is a fragmentary sectional elevation of a modified construction, 7

Figure 3 is a diagrammatic sectional elevation of another form,

Figure 4 is a similar view of yet another form,

Figure 5 is a diagrammatic end elevation of the form shown in Figure 4,

Figure 6 is a fragmentary cross-section on the line VIVI, Figure 5, showing components in the normal position during operation of the servo,

Figure 7 is a fragmentary cross-section on the line VII-VII, Figure 5, showing further components in thenormal position during operation of the servo,

Figure 8 is a fragmentary view similar to Figure 6, showing the components in the emergency position, and

Figure 9 is a fragmentary view similar to Figure 7, showing the corresponding components in the emergency position.

Referring to Figure 1 of the drawings, a jack body I0 anchored to the aircraft at points I I contains a jack piston I2 having two hollow stems I3, I4 extending axially on either side of it, of which I4 is connected by a rod I5 With the control surface I5 to be actuated, and termed the actuating stem, the other, I3, being free, and termed the free stem. The hollow stems I3, I4 are pierced radially at I6, I'I respectively to provide fluid communication between their interiors I8, I9 and the corresponding chambers 20, 2I of the jack cylinder Ill.

Within the jack piston I2 and the stems I3, I4 is a reaction piston 22 which passes slidably through the jack piston l2, and is sealed at 23 and 24. This reaction piston 22 extends axially along the stems, and with them forms two chambers I8, I9, which are separated from one another at the point where the reaction piston 22 passes through the jack piston I2, but which are in fluid communication respectively with the two chambers 20 and 2| of the jack cylinder ID. The reaction piston 22 is further formed with two lands 25, 26 at a point just before it emerges from the open end 21 of the free stem I3, thereby sealing the chamber I8 within thefree stem and also forming a gallery 28 between the lands 25, 26. There are therefore three chambers formed by the jack piston I2 and its stems I3, I4 and the reaction piston 22, namely, a chamber I9 within the actuating stem I4, in fluid communication through the passages ll with the jack chamber 2| around it; a chamber I8 within the free stem I3, in fluid communication through the passages I6 with the other jack chamber 26, which is around it; and a gallery 28 within the free stem I3 at its free end, and bounded by lands 25, 26 on the reaction piston 22. Further, the reaction piston 22 has an axial passageway 29 and ports 30, 3| at the ends thereof serving to establish fluid communication between the gallery 28 and the chamber I9 within the actuating stem.

Mounted on and near the free end 21 of the free stem I3 is a selector valve 32 comprising a valve operating rod 33, and body 34, an inlet port 35 in communication with the hydraulic pressure pipeline of the aircraft, an outlet port 35- in communication with the return pipeline, and two ports 36, 31 in communication respectively with the gallery 28 and with the chamber I8 in the free stem I3. The valve rod 33 of the selector valve 32 is connected directly with the pilot's control 38. A link 39 in the connection, consisting of a sleeve slidably mounted on the free end 42 so as to be kept in alignment therewith, is slotted as at 40, and engages with a pin 4| carried by the free end 42 of the reaction piston 22, thus forming a lost-motion device connecting the pilots control 38 with the reaction piston 22. Slot 4|] may have a notch 40 in its side for a purpose to be described presently.

There are therefore two alternative fluid paths for the hydraulic pressure, namely, through the first port 36 of the selector valve 32 to the gallery 28 in the free stem I3, and thence via the axial passageway 29 in the reaction piston 22, the chamber I9, and the passage I1 to the jack cham,- ber 2| around the actuating stem I4; or through the second port 31 of the selector valve 32 to the chamber I8 in the free stem I3, and thence, through the passage IE, to the: jack chamber 20.

In operation, initial movement of the pilots control 38 moves the valve rod 33 and places one or other of the selector valve ports 36, 31 in communication with the hydraulic pressure inlet 35. This admits fluid pressure to one of the chambers I8, IS, in the jack piston I2 and to the corresponding jack chamber, driving the jack piston I2 in the direction selected, and driving the reaction piston 22 in the opposite direction. This movement of the reaction piston 22 takes up the remaining lost motion between the pin 4| and slot 40 and is then felt by the pilot, who must resist it to keep the valve 32 open.

The efforts exerted by the servo and the pilot are in the ratio of the cross-sectional areas of the jack chamber 20 or 2| and the reaction piston chamber I8 or I9, and may be predetermined to any desired value by the arrangement of suitable dimensions of the bores.

When the pilots control member 38 is initially displaced, say to the left in Figure 1, the valve rod 33 is also moved in the same manner via 39, but the valve-carrying member I3 and pin I4 are not moved. Thus, initially, only the valve rod 33 moves, such movement bringing the pin 4| to the end of the slot 40, when the valve will only be just open. Further movement of the control 38 will open the valve fully and also displace the reaction piston 4222 which is endeavoring to travel in the opposite direction, under the influence of the pressure which has been admitted into annular chamber I9 by the initial valve opening. The same pressure is also operative in chamber 2| of the jack and causes member I4 to travel in the same direction as that selected by member 38 and valve 32. At the instant that movement of member 33 is stopped, and with it 39 and 33, the pressure is still being fed into chamber 2|, causing I4 to continue its movement. As the valve body 34 is rigidly attached to I4 via I3 and I2, the valve body must move relatively to the stationary valve rod 33, thereby closing the valve port originally selected open.

The pin 4| will remain at the end of the slot 40 until the valve is selected in the opposite sense, when it will move to the other end of slot.

If desired, the lost motion'between pin 4| and slot 40 can be dispensed with, e. g. by a slight rotation of stem 42 so that pin 4| on piston 22 engages recess 4K1 at the side of slot 40. The provision of this slot and pin connection obviates the necessity for moving the reaction piston 42,22 when operating valve rod 33, and permits valve operating loads to be much smaller than would otherwise be the case. In case of pressure failure, leaving only manual efiort available, the pin and slot can be locked together by engaging notch 4|] with the pin, thus reducing the lost motion in the control.

Figure 2 shows a modification of the construction illustrated in Figure 1. The body of the jack piston I2, having a smaller internal diameter than that of the actuating stem I4, is employed as a stop to limit the axial travel of the reaction piston 22 relatively to the jack piston,

and a further stop I4, consisting of an inwardly directed flange I4 integral with the actuating stem I4, is provided to restrict the axial travel of the reaction piston 22 away from .the jack piston I2.

In the event of failure of the hydraulic pressure, a control run is thus provided between the pilots control and the control surface to be actuated, it being understood that in addition to the lost motion between the pin 4| and slot 40 there is also lost motion to be taken up between the reaction piston 22 and oneor other of the stops, after which there is direct manual control.

If desired, the lost motion between the pin 4| and slot 40 can be dispensed with, in the same manner as explained above with respect to Fig. -1.

Referring to an alternative embodiment shown in Figure 3, the reaction piston chamber is formed at the free end of the free stem I3, and is sealed from the interior 43 of the jack piston I2 by an internal flange 44 through which passes a stem 45 attached to one side of the reaction piston 22. The selector valve 32 controls two fluid paths, one of which connects the hydraulic pressure line 46 with the reaction piston chamber 41, and also, by means of a flexible pipe connection 49, with the jack chamber 2|. The fluid return line 5| is then connected with the reaction piston chamber 48 and, by the flexible pipe connection 56, with the jack chamber 20. The other fluid path joins the hydraulic pressure line 46 with the other reaction piston chamber 48 and by means of the flexible pipe connection 50, with the jack chamber 20, corresponding return connections being made with the return line 5|. The stem52 of the reaction piston is formed with two stop rings 53, 54, the former within the reaction piston chamber 41 and the latter outside it, and there is a seal 55, at the point where the end of the reaction piston emerges from the chamber 41, which acts as an abutment causing the stop rings 53, 54 to limit the axial travel of the. reaction piston 22. The amount of travel permitted is sufiicient for normal operation of the servo, but if the hydraulic pressure fails, the pilot can operate the control surface manually since, after he has taken up the lost motion due to the axial travel of the reaction piston 22, further movement of the control column 38 is trans- 1 mitted by one of the stop rings 53, 54 to the free stem l3 of the jack piston, and thence by the rod l5 to the control surface. 9 a

Figureslto 9 show yet another form of the invention, in which the jack body Ill, instead of being permanently anchored to the aircraft, is slidably mounted in an anchorage 56 so as to be capable of axial movement therein. The anchorage 56 is formed with a chamber 51 (see Figures 6 and 7) containing a locking piston 58 capable of axial movement against a compression spring 59 when fluid pressure is admitted through a passage 60 at one end of the chamber 51. The jack body In is formed with an annular depression or groove 6| at its middle.

Passing radially through the chamber 51 of the jack anchorage 56 is the stem 62 of a cut off valve 63 of the piston type, the stem being held in a valve body 64 and pressed radially inwards against the jack body ID by a compression spring 65, the inner end of the cut ofi valve terminating in a roller 66 to minimize friction when the jack body I8 moves axially. The valve body 64 and stem 62 are bored to present an unobstructed passage for fluid pressure when the roller 66 is in the annular depression 6| of the jack body [8, that is, when the jack body is centrally disposed relatively to the anchorage 56, but when the jack body is out of the central position, the roller 66 is lifted out of the annular depression BI and the stem 62 is raised, thus obstructing the passage. One side of the cut off valve 63 is connected with the hydraulic pressure line 46, and the other side with the passage 60 admitting pressure to one end of the chamber 51 of the jack anchorage 56.

Within the jack anchorage 56 and rigidly attached thereto is a collet 61 embracing the jack body I!) and having an axial slot to accommodate and allow relative movement of the out 01f valve roller 66. The collet 6'! has two resilient blades terminating in jaws 68 which tend tospring radially outwards, but which can be forced inwards, by ramps 69 on the inner wall of the locking piston 58, to engage in the annular depression 6| in the jack body II].

In normal operation the jack body I8 is centrally disposed in the anchorage 56, and therefore the cut off valve roller 66 is in the annular depression 6| and the cut off valve is open, as shown in Figure 6. Fluid pressure is hence admitted through the passage 60 to the jack anchorage chamber 57, and forces the locking piston 58 against its compression spring 59 and the ramps 69 on its inner wall against the collet jaws 68, looking them in engagement with the annular depression 6| in the jack body ID, as shown in Figure 7. The jack body In is thus kept locked to the jack anchorage 56 and the servo operates in the manner previously described.

Should the hydraulic pressure fail, however, the locking piston 58, under the force of its compression spring 59, expels the fluid from the jack anchorage chamber 51 and allows the collet jaws 68 to spring outwards and hence unlock the jack body ID from the jack anchorage 56, as shown in Figure 9i The entire servo mechanism is therefore now slidable within the jack anchorage, and may be used by the pilot in an emergency as an ordinary link in the control run. When the jack body I8 is moved from the normal central position it raises the roller 66 out of the annular depression 6| and closes the cut off valve as shown in Figure 8, thus isolating the locking piston 58.

The out ofi valve may alternatively be of the poppet type.

The advantages of the systems of Figures 4 to 9 are as follows:

(1) They provide a safeguard against valve or jack seizures (from any cause) when used. in conjunction with pressure systems where the pressure feed to the valve can be turned off and released at operators will. Thus in case of seizure, when the operator finds he is unable to move the control, he turns the pressure off and thus releases the mechanism from its anchorage in the axial sense. The control can then be moved manually as a whole.

(2) They provide a means for use in lightly powered controls where assistance is required under one set of conditions, such as, maximum maneuverability at high speeds, and where assistance is not required (on some aircraft) as when landing and during other low-speed flying. In such applications the pressure could be switched on or off at operators will.

I claim:

1. In an arrangement for actuating a control surface, hydraulic servo means comprising a jack cylinder, a jack piston within said cylinder, connecting means between said jack piston and said control surface, a reaction piston within cylinder means formed in said jack piston, a source of fluid pressure, a selector valve arranged to control the admission of fluid pressure to said jack cylinder, a pilots control connected directly with said selector valve, a lost motion device connecting said pilots control and reaction piston and permitting limited relative axial movement in each direction between said control and said reaction piston, and means admitting sa'id fluid pressure into the cylinder means to act on said reaction piston simultaneously with, but in a contrary direction to, the admission of fluid pressure to said jack piston, so causing the reaction piston to produce a sense of feel" at said pilots control.

2. In an arrangement for actuating a control surface, hydraulic servo means as claimed in claim 1, the jack piston having internal stops limiting the travel of the reaction piston relatively to the jack piston, so providing a direct connection between the pilots control and the control surface to be actuated if the fluid pressure fails.

3. In an arrangement for actuating a control surface, hydraulic servo means as claimed in claim 1, the reaction piston being formed with an external and an internal stop, near the point where it emerges from the jack piston, limiting the travel of the reaction piston relatively to the jack piston, so providing a direct connection between the pilots control and the control surface to be actuated if the fluid pressure fails.

4. In an arrangement for actuating a control surface, hydraulic servo means comprising a jack, cylinder anchorage, a jack cylinder slidably mounted within said anchorage, a source of fluid pressure, means actuated by said fluid pressure and adapted to lock the jack cylinder relatively to the anchorage, a jack piston within said jack 7 cylinder, connecting means between:v said jack piston and said control surface, a reaction piston within cylinder means formed in. said jack piston, a, selector valve arranged to control the admission of fluid pressure to said jack cylinder, a pilots control connected directly with said selector valve, a lost motion device connecting said pilot's control and reaction piston and permitting limited relative axial movement in each direction between said control and said reaction piston,

5. In an arrangement for actuating a control surface, hydraulic servo means as claimed in claim 4, the jack cylinder being formed with a: circumferential groove and the anchorage being provided with a outlet and a piston arranged to move said collet, under the influence of the h-y draulic pressure, into said groove and so anchor the jack cylinden.

CHARLES REGINALD CHURN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,258,337 Im-blum Mar; 5, 1918 2,197,075 Fitzgerald Apr. 16, 1940 2,307,910 Baade Jan, 12, 1943 2,393,585 Boynton Jan. 29, 1946 

